1. Field of the Invention
The present invention relates to a printing control apparatus, a printing apparatus, and a printing method.
2. Description of the Related Art
A printing apparatus that forms an image on a print medium by ejecting ink onto the print medium while scanning a print head including a plurality of ejection port arrays in which a plurality of ejection ports that eject ink of the same color are arranged in a certain array direction is known. The plurality of ejection port arrays are arranged in a direction crossing to the array direction of the ejection ports, and the print head is scanned in the direction crossing to the array direction of the ejection ports.
In these years, it is desired to improve the printing speed of such a printing apparatus, and the length of the print head is being increased to achieve this goal. In one of known methods for increasing the length of the print head, a print head (hereinafter referred to as an overlap head) in which a plurality of ejection port arrays are sequentially arranged in an array direction of a plurality of ejection ports is configured by providing portions (hereinafter referred to as overlap portions) capable of printing the same pixel rows on a print medium using certain numbers of ejection ports arranged at ends of two ejection port arrays adjacent to each other in the array direction of the plurality of ejection ports that ejects ink of the same color. According to this overlap head, the length of the print head may be increased by arranging a plurality of short ejection port arrays.
It is known when an image is printed using the overlap head, unevenness might occur in a region of the print medium in which the ejection ports arranged in the overlap portions have performed printing and image quality might deteriorate. The types of unevenness include unevenness caused by errors in the installation positions of the ejection port arrays or errors in the manufacturing process of the ejection ports and unevenness caused by differences in the ejection timing of ink from the ejection ports arranged in the overlap portions of the ejection port arrays. In Japanese Patent Laid-Open No. 2009-12390, it is disclosed that the amounts of ink ejected from the ejection ports in the overlap portions are made smaller than the amounts of ink ejected from the ejection ports in regions other than the overlap portions in order to suppress the above-described unevenness caused by differences in the ejection timing.
On the other hand, when an error has occurred in conveying of the print medium between operations of scanning of the print head, a black stripe or a white stripe might be formed at a boundary between a portion printed immediately before the conveying of the print medium and a portion printed immediately after the conveying of the print medium and the quality of the printed image might deteriorate. In Japanese Patent Laid-Open No. 2007-268825, it is disclosed that printing is performed such that the shape of the boundary between portions printed before and after the conveying becomes the shape of waves so that the stripe does not stand out.
However, because the combinations between the ejection ports included in the overlap portion between two ejection port arrays are fixed in the overlap head disclosed in Japanese Patent Laid-Open No. 2009-12390, it is assumed that positions at which unevenness caused by the overlap portions occurs remain the same on the print medium. Therefore, it is difficult to sufficiently suppress the unevenness caused by the overlap portions of the overlap head using a method for changing density, which is disclosed in Japanese Patent Laid-Open No. 2009-12390.
Therefore, the inventors have changed the positions of the ejection ports in the overlap portions in the array direction in accordance with the scanning of the print head. As a result, the positions at which the ejection ports in the overlap portions perform printing have changed on the print medium, thereby making it possible to keep the unevenness caused by the overlap portions from standing out.
Furthermore, the position of the boundary between the region printed in scanning before the conveying of the print medium and the region printed in print scanning after the conveying of the print medium has been changed in the array direction as the scanning direction has changed. As the inventors have tried to simultaneously suppress the unevenness that occurs in a region in which the ejection ports in the overlap portions perform printing and the stripe formed in a region in which printing is performed before and after the conveying of the print medium in this manner, a new problem has arisen.
This problem will be described in detail hereinafter.
FIG. 1 is a diagram illustrating a problem to be solved by the present invention.
An overlap head 1000 is configured by arranging a plurality of ejection port arrays in a certain array direction (hereinafter referred to as a Y direction). Here, among the plurality of ejection port arrays, two ejection port arrays 1100 adjacent to each other in the Y direction are arranged at different positions in the Y direction and different positions in a cross direction (hereinafter referred to as an X direction), which is crossing to the Y direction such that certain numbers of ejection ports arranged at ends of the two ejection port arrays 1100 may perform printing in the same region of a print medium 3 in the same scanning.
An image is formed on the print medium 3 by alternately performing print scanning, in which ink is ejected while scanning the overlap head in the X direction, and sub-scanning, in which the print medium 3 is relatively conveyed in the Y direction, which is a conveying direction.
Here, as illustrated in FIG. 1, a shape 1200 of waves is formed by performing printing such that the position of the boundary between two regions in which the two ejection port arrays 1100 perform printing is changed in accordance with the scanning of the above-described overlap head 1000. In addition, printing is performed such that the boundary between regions in which printing is performed in two consecutive operations of scanning before and after the conveying has a shape 1210 of waves. In this case, the shape 1200 of waves caused by the printing performed by the overlap portions and the shape 1210 of waves caused by the printing performed in two operations of scanning might be the same, thereby accentuating each other as unevenness. Such unevenness stands out especially when the shape 1200 of waves and the shape 1210 of waves have been superimposed in the same region of the print medium 3.